From db99baac354d08196a9e64790fa552eb14e932d5 Mon Sep 17 00:00:00 2001
From: Ben Adams <thundercat@illyriad.co.uk>
Date: Fri, 7 Sep 2018 22:08:08 +0100
Subject: [PATCH] Don't capture AsyncLocals onto Timers (#2904)

---
 src/Common/TimerAwaitable.cs                  | 21 ++++++++++++++++++-
 .../Internal/AckHandler.cs                    | 21 ++++++++++++++++++-
 2 files changed, 40 insertions(+), 2 deletions(-)

diff --git a/src/Common/TimerAwaitable.cs b/src/Common/TimerAwaitable.cs
index d2e0005bcf..ee6cb0fd23 100644
--- a/src/Common/TimerAwaitable.cs
+++ b/src/Common/TimerAwaitable.cs
@@ -40,7 +40,26 @@ namespace Microsoft.AspNetCore.Internal
 
                     if (_timer == null)
                     {
-                        _timer = new Timer(state => ((TimerAwaitable)state).Tick(), this, _dueTime, _period);
+                        // Don't capture the current ExecutionContext and its AsyncLocals onto the timer
+                        bool restoreFlow = false;
+                        try
+                        {
+                            if (!ExecutionContext.IsFlowSuppressed())
+                            {
+                                ExecutionContext.SuppressFlow();
+                                restoreFlow = true;
+                            }
+
+                            _timer = new Timer(state => ((TimerAwaitable)state).Tick(), this, _dueTime, _period);
+                        }
+                        finally
+                        {
+                            // Restore the current ExecutionContext
+                            if (restoreFlow)
+                            {
+                                ExecutionContext.RestoreFlow();
+                            }
+                        }
                     }
                 }
             }
diff --git a/src/Microsoft.AspNetCore.SignalR.Redis/Internal/AckHandler.cs b/src/Microsoft.AspNetCore.SignalR.Redis/Internal/AckHandler.cs
index b455d0427d..c5502e28a2 100644
--- a/src/Microsoft.AspNetCore.SignalR.Redis/Internal/AckHandler.cs
+++ b/src/Microsoft.AspNetCore.SignalR.Redis/Internal/AckHandler.cs
@@ -19,7 +19,26 @@ namespace Microsoft.AspNetCore.SignalR.Redis.Internal
 
         public AckHandler()
         {
-            _timer = new Timer(_ => CheckAcks(), state: null, dueTime: _ackInterval, period: _ackInterval);
+            // Don't capture the current ExecutionContext and its AsyncLocals onto the timer
+            bool restoreFlow = false;
+            try
+            {
+                if (!ExecutionContext.IsFlowSuppressed())
+                {
+                    ExecutionContext.SuppressFlow();
+                    restoreFlow = true;
+                }
+
+                _timer = new Timer(state => ((AckHandler)state).CheckAcks(), state: this, dueTime: _ackInterval, period: _ackInterval);
+            }
+            finally
+            {
+                // Restore the current ExecutionContext
+                if (restoreFlow)
+                {
+                    ExecutionContext.RestoreFlow();
+                }
+            }
         }
 
         public Task CreateAck(int id)